I. Field of the Invention:
The present invention relates to an improvement in a lumbar support device which is arranged in the seatback to support a lumbar portion of an occupant of the seat. The lumbar support device provides the seat occupant with a comfortable feeling while sitting.
II. Description of the Prior Art
It has been desired that a seat occupant is stably held during operation of the motor vehicle. It is also desirable that the seat occupant feel comfortable while sitting. Ideally, the seat is designed to prevent the occupant from suffering a marked fatigue even after a lengthy period of sitting. In order to obtain these desired merits, the seat is equipped at various places with support devices.
These support devices are, for example, a side support device which is arranged to support the side of the occupant and a lumbar support device which supports a lumbar portion of the occupant; these support devices are known.
In the lumbar support device, a pad member having a suitable hardness is movably disposed in the seatback at a position which faces the lumbar portion of the occupant. By moving the pad member forward or rearward, a lower portion of the seatback is swelled out at need.
Various lumbar support devices are known. For example, Japanese Utility Model First Provisional Publication 51-163224 and Japanese Patent First Provisional Publication 57-19965 disclose a cushion member in the back of the seat which is adjustable for hardness by combining a spring member located behind the cushion member and a threaded shaft adjusting means. In this lumbar support device, the hardness of the cushion member can be steplessly adjusted by the threaded shaft adjusting means, so that fine control is easily achieved. In addition, excellent impact resistance and marked adjusting stroke are obtained.
However, the above-mentioned lumbar support device has the following drawbacks. That is, when the spring member is assembled, one end portion of the spring member is in contact with the back side surface of the cushion member. Therefore, a troublesome and complicated assembly procedure is necessary. A middle portion of the spring member must be formed to have a coiled portion and the coiled portion is pivotally fitted to a pin which is fixed to a bracket in the seatback. In addition, numerous parts and steps are needed for the assembly of the device which cause an increase in production cost.
Furthermore, in the above-mentioned lumbar support device, the arrangement to pivotally connect the middle portion of the spring member to the pin and the other arrangement to connect the other end of the spring member to the threaded shaft adjusting means limit the usable space. The entire construction of the device tends to have a large size, so that design freedom is limited. Thus, solving these drawbacks has been hitherto desired.
Additionally, in the lumbar support devices taught by the prior art, the spring member whose coiled portion is pivotally connected to the pin of the seatback is swingably moved by the operation of the threaded shaft adjusting means. The other end portion of the spring member is moved by the operation of the threaded shaft adjusting means so that the other end portion of the spring member adjusts the degree of movement of the cushion member.
Thus, the resilient force of the spring member is kept constant, so that for achieving an effective lumbar supporting function, it becomes necessary to enlarge the stroke by a certain degree. Considering this, a control knob which must be turned many times for driving the threaded shaft adjusting means is not suitable. In addition, drivability of the control knob is poor.